Sheet stacking device and sheet processing apparatus

ABSTRACT

In a sheet stacking device including a sheet stacking section, a holding member for holding sheets on the sheet stacking section, and a driving device for moving the holding member to the holding position and retreating position, the holding of the holding member which retreats when a sheet is being fed in and which holds the sheet when the sheet has reached, is canceled on the basis of approaching information of a succeeding sheet.

This application is based on Japanese Patent Application No. 2006-233323filed on Aug. 30, 2006 in Japanese Patent Office, the entire content ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a sheet stacking device and a sheetprocessing apparatus and more particularly to an art for suppressinguplift of sheets of paper at the sheet stacking step.

In a copier and a printing device, sheets of paper with images formedare stacked on a stacking device, and when conducting post-processing tothe stacked sheets of paper or stacking a large amount of sheets ofpaper, a sheet holding device for suppressing uplift of sheets of paperis often used.

In Patent Document 1, a sheet stacking device for suppressing uplift ofsheets of paper and aligning sheets of paper by using a switching gatefor switching between a holding position for holding sheets of paper anda guiding position for guiding entry of sheets of paper and by using amoving aligning member for pressing the rear ends of sheets of paper isproposed.

In Patent Document 1, the switching gate is set at the position forguiding entry of sheets of paper at the sheet entry stage, and is set atthe sheet holding position at the stage of arrival of sheets of paper atthe sheet stacking section, and then is set at the position for guidingat the sheet entry stage after finishing of alignment by the aligningmember, that is, at the position for guiding entry of sheets of paper.

When continuously conveying sheets of paper and stacking many sheets ofpaper on the sheet stacking section, the aforementioned step is executedrepeatedly.

In the sheet stacking device in Patent Document 1, the sheet holding iscanceled when the alignment is finished, so that the elapsed timebecomes long until the next sheet reaches the sheet stacking section andthe holding member starts to hold the sheet of paper, thus the sheet ofpaper may be uplifted.

Therefore, a problem arises that a sheet bundle becomes thick and sometroubles occur in the post processing for the sheet bundle and thequality of a booklet prepared by the bookbinding process isdeteriorated.

Further, due to uplift of sheets of paper, satisfactory alignment maynot be realized.

Patent Document 1: Unexamined Japanese Patent Application PublicationNo. 2001-322760

SUMMARY

One aspect of the present invention is as indicated below.

1. A sheet stacking device including a sheet stacking section, a holdingmember for holding sheets on the sheet stacking section, and a drivingdevice for moving the holding member to the holding position andretreating position, wherein:

the sheet stacking device further has a control device for controllingthe driving device, and the control device sets the holding member atthe retreating position at the stage of conveying sheets to the sheetstacking section, sets the holding member at the holding position at thestage of arrival of sheets at the sheet stacking section, andfurthermore, on the basis of information of approaching of a succeedingsheet to the sheet stacking section, the control device controls to setthe holding member at the retreating position.

2. A sheet processing apparatus including a sheet stacking device ofabove item 1 and a processing device for processing sheets stackedthereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing the whole image forming system relating tothe embodiment of the present invention.

FIG. 2 is a drawing showing the constitution of a reverse section 40 anda sheet stacking section 50 of a bookbinding device B.

FIG. 3 is a drawing showing the drive control system of a holding member510.

FIG. 4 is a flow chart of drive control of the holding member 510.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be explained referring to a preferredembodiment shown in the drawings. However this invention is not limitedto the preferred embodiment.

FIG. 1 is a view of the entire image forming system relating to apreferred embodiment of the present invention.

The image forming system includes image forming apparatus A andbookbinding apparatus B.

Image forming apparatus A electrophotographically forms images on sheetsand is equipped with image forming section A1, document feeder A2, andimage reader A3.

Image forming section A1 has charging unit 2, exposing unit 3,developing unit 4, transfer unit 5A, separating unit 5B, and cleaningunit 6 around drum-shaped photoreceptor 1. These electrophotographicunits perform charging, exposure, development, and transferring in orderto form a toner image on the surface of photoreceptor 1 and an image onsheet S1.

Sheets S1 are stored in three sheet supply trays 7A, and delivered oneby one from sheet supply trays 7A to transfer unit 5A. Sheet S1 receivesa toner image there from photoreceptor 1 by transfer unit 5A.

Sheet S1 with a toner image transferred on it is delivered throughfixing unit 8 and fixed there. Fixed sheet S1 is ejected by ejectionrollers 7C or delivered to sheet re-feeding path 7E.

For face-down sheet ejection of one-side printing, face-up sheetejection of one-side printing or front side image forming of both-sideimage forming, switching gate 7D switches to guide sheet S1. That is,when sheet S1 is ejected with its face up, switching gate 7D deliverssheet S1 straight. When sheet S1 is ejected with its face down or whensheet S1 has images on both surfaces, switching gate 7D delivers sheetS1 downward.

When sheet S1 is ejected with its face down, sheet S1 is guideddownward, switched back to move up, and ejected by ejection rollers 7C.

In the both-side image forming, sheet S1 is guided downward, turnedupside down with a switchback, delivered again to a transfer sectionwhich includes transfer unit 5A through the sheet re-feeding path 7E,and receives another image on the other surface of the sheet.

Document feeder A2 feeds documents one by one to a reading position.Image reader A3 reads the image on a document which is fed from documentfeeder A2 or placed on document table 9 and generates an image signal.

Bookbinding apparatus B is an apparatus which bundles plural sheets sentfrom image forming apparatus A into a bundle of sheets, bonds a coversheet to the sheet bundle to form a booklet. On the followingexplanation, the sheet on which an image is formed in image formingapparatus A and which is fed to bookbinding apparatus B is called sheetS1, the cover sheet is called cover sheet S2 and the booklet whereinsheets are bonded with the cover sheet is called booklet S3.

The bookbinding apparatus B described in the figure is an example ofsheet processing apparatuses and the sheet processing apparatusesinclude various types of sheet processing apparatuses such as aprocessing apparatus for stapling a bundle of sheets with staples and atape-binder which binds a bundle of sheets with a tape.

Bookbinding apparatus B is equipped with reverse section 40, sheetstacking section 50, adhesive coating section 60, a bonding device tobond a cover sheet to a bundle of sheets (composed of cover sheetsupporting section 90), further with conveying section 10, sheetejection tray 20, cover sheet storage section 80 and booklet ejectingsection 100.

Sheet S1 ejected from image forming apparatus A is delivered toswitching gate 11 in conveying section 10. The switching gate 11 changessheet paths to send sheet S1 to sheet ejection tray 20 via ejection path12 or to reverse section 40. In the non-bookbinding mode, sheets S1 areejected to sheet ejection tray 20.

In the bookbinding mode, sheet S1 is sent to reverse section 40 viaconveying path 13, switched back by reverse section 40, and delivered tosheet stacking section 50. A preset number of sheets S1 are stacked insheet stacking section 50 and when the preset number of sheets S1 havebeen stacked, sheet stacking section 50 is rotated and the bundle ofsheets S1 is held almost vertically.

Adhesive coating section 60 applies adhesive to the bottom surface ofbundle of sheets S1 which is held vertically by sheet stacking section50.

Cover sheet S2 is brought into contact with the bundle of sheets S1which has been coated with adhesive to be bonded to it by means of thebonding device.

Booklet S3 made by bonding cover sheet S2 to the bundle of sheet S1 isejected to booklet ejecting section 100.

In the bookbinding device B, a sensor SE1 for detecting sheets S1 in thesheet entrance section, a sensor SE2 for detecting the sheets S1 in thesheet ejection section to the sheet reverse section 40, a sensor SE3 fordetecting the sheets S1 in the feed-in section (the neighborhood on theupstream side of the sheet receiving section) of the sheet stackingsection 50, and a sensor SE4 on the bottom of the sheet stacking section50 are installed.

On the basis of sheet detection signals of the sensors SE1 to SE4, sheetconveyance control and process control are executed in the bookbindingdevice B.

FIG. 2 is a drawing showing the constitution of the reverse section 40and sheet stacking section 50 of the bookbinding device B.

The sheets S1 conveyed on a conveying path 13 are ejected by sheetejection rollers 14 and moved up on an inclined reverse guide 402 viaconveying rollers 401, and then the conveying rollers 401 invert therotation and convey the sheets S1 downward.

Numeral 406 indicates conveying rollers for conveying the sheets S1 fromthe reverse section 40 to the sheet stacking section 50.

The sheets S1 conveyed downward are dropped and stacked on the sheetstacking section 50. The sheet stacking section 50 includes a supportplate 502 and a receiver plate 506 and the sheets S1 which have moveddown in the reverse section 40 are supported by the support plate 502and receiver plate 506 in the inclined state.

The sheets S1 sequentially ejected from an image forming apparatus A arestacked on the sheet stacking section 50 and a sheet bundle SS isformed. The number of the sheets S1 composing the sheet bundle SS is setby the setting section (not illustrated) of the image forming apparatusA. Numeral 505 indicates an aligning plate for aligning the side edgesof sheets.

Numeral 510 indicates a holding member for suppressing uplift of thesheets S1 conveyed into the sheet stacking section 50 and it isinstalled in the sheet feed-in section of the sheet stacking section 50.The holding member holds the sheets S1 conveyed into the sheet stackingsection 50 at the solid line position and moves to the dotted lineposition, thereby retreats from the conveying path of the sheets S1 tothe sheet stacking section 50, and enables entry of the sheets S1 intothe sheet stacking section 50.

At the stage of completion of stacking the sheets S1 of the number ofsheets composing the sheet bundle SS, a holding plate 503 operates andholds the bundle of the sheets S1.

The sheet stacking section 50 rotates around a shaft 501 while holdingthe bundle of the sheets S1 and changes the state of the bundle of thesheets S1 from the inclined state to the perpendicular state.

FIG. 3 is a drawing showing the drive control system of the holdingmember 510.

When a plunger 512 is pulled by turning on a solenoid 511, a shaft 510Ato which the holding member 510 is fixed is rotated clockwise in FIG. 3,thus the holding member 510 is set at the holding position. When thesolenoid 511 is turned off, the plunger 512 moves in the direction ofthe arrow to rotate the shaft 510A, and the holding member 510 retreatsto the dotted line position shown in FIG. 2, thus the conveying path forconveying the sheets S1 to the sheet stacking section 50 is formed.Although the holding member 510 is composed of two pieces in the figure,it can be composed of one piece, of course. Therefore the singular nameis generically used for the holding member 510 in this document.

At the stage of conveying the sheets S1 into the sheet stacking section50, the holding member 510 is set at the dotted retreating positionshown in FIG. 2, thus the sheet feed-in path into the sheet stackingsection 50 is formed, and at the stage of having stored the sheets S1 inthe sheet stacking section 50, the holding member 510 is set at thesolid line position shown in FIG. 2 and holds the sheets S1.

Such drive control of the holding member 510 is executed by a controldevice 513. The drive control of the holding member 510 will beexplained by referring to FIG. 4.

FIG. 4 is a flow chart of the drive control.

At STEP 1, existence of sheets in the sheet stacking section 50 ischecked. STEP 1 is executed on the basis of a sheet detection signal ofthe sensor SE4 installed on the bottom of the sheet stacking section 50.

When there are some sheets S1 in the sheet stacking section 50, asexplained later, the holding member 510 is set at the working position(YES at STEP 1), while there are no sheets S1 (NO at STEP 1), thesolenoid 511 is off, and the holding member 510 is at the dotted lineposition, and the sheet feed-in path to the sheet stacking section 50 isformed (STEP 2).

By passing detection signal of a sheet rear end by the sensor SE3,conveying of sheets into the sheet stacking section 50 is detected (STEP3), and the aligning member 505 is driven (STEP 4), and the solenoid 511is operated, and the holding member 510 is rotated to the solid lineposition shown in FIG. 2 and is set at the sheet holding position. Bydoing this, uplift of the sheets S1 newly introduced into the sheetstacking section 50 is eliminated.

The number of sheets stacked in the sheet stacking section 50 is countedon the basis of the sheet detection signal of the sensor SE3 and at thestage of arrival of the counted value at the set number indicating thenumber of sheets S1 composing the sheet bundle SS (YES at STEP 6), theprocess goes to the bookbinding process at STEP 7.

When the counted value does not arrive at the set number of sheets (NOat STEP 6), at STEP 11, whether succeeding sheets are approaching thestacking section 50 or not is monitored. However when a stop signal isreceived at the previous stage (YES at STEP 8), the holding member 510is set at the retreating position (STEP 9).

The stop signal at STEP 8 is a stop signal received by a control deviceCR mainly from the image forming apparatus A, and as a case that such astop signal is sent, there are a case that the sheets S1 on the sheetsupply tray 7A (shown in FIG. 1) of the image forming apparatus A havebeen all fed out and a case that a jam occurs in the image formingapparatus A. In addition, there are cases that a failure such as a jamoccurs in the bookbinding device B and cover sheets S2 have been all fedout.

When the stop signal is received (YES at STEP 8), the holding member 510is set at the retreating position (STEP 9). After waiting for andreceiving a stop cancelling signal (STEP 10), the holding member 510 isset at the holding position (STEP 11).

When there is no stop signal at STEP 8 or after STEP 11, the holdingmember 510 is set at the holding position and in this state, whether ornot the next sheet S1 is approaching the sheet stacking section ismonitored (STEP 12).

The monitoring at STEP 12 is executed on the basis of the passingdetection signal of the rear end of sheets S1 by the sensor SE2installed on the upstream side of the reverse section 40. Namely, STEP12 is a step for detecting approaching information of conveying thesheets S1 to the sheet stacking section 50 and for obtaining theapproaching information, a detection signal of the sensor SE2 installedon the upstream side is used instead of the sensor SE3 installed in theneighborhood of the feed-in section of the sheet stacking section 50.

When approaching of sheets to the sheet stacking section 50 is detected,the process is returned to STEP.2, and the holding member 510 is set andretreated at the dotted line position shown in FIG. 2, and the sheetfeed-in path to the sheet stacking section 50 is formed.

At the control step shown in FIG. 4, the sheets stored in the sheetstacking section 50 are held by the holding member 510. Uplift of thesheets is eliminated, and the sheets are continuously held immediatelybefore the next sheet enters and at the stage of detection ofapproaching of the next sheet S1, the holding is canceled. Thus thesheets held once are prevented from uplifting, and a sheet bundle in astate in which the sheets and sheets are closely adhered to each otheror a state close to this state is formed.

Therefore, the problem is solved that the quality of a booklet bound byconducting processing to the sheet bundle is deteriorated.

The approaching information of the sheets S1 to the sheet stackingsection 50 is obtained from a sensor installed on the upstream side ofthe sheet stacking section 50, for example, SE2. However the approachinginformation can be obtained from a sensor other than SE2. For example, adetection signal of the sensor SE1 installed in the sheet entrancesection of the bookbinding device B can be used. In this case, controlis executed for canceling the holding of the holding member 510 after alapse of a predetermined period of time after the sheet detection signalof the sensor SE1 comes.

According to the present invention, the holding of the sheet holdingmember is canceled on the basis of the sheet approaching information tothe sheet stacking section, so that the sheet holding is continuedimmediately before arrival of the sheets at the sheet stacking section,and the period of time when the holding is cancelled is shortened. As aresult, uplift of sheets in the sheet stacking section is prevented, anda sheet bundle composed of sheets closely adhered to each other isformed, and the post processing is performed smoothly, and the qualityof output of the sheet processing apparatus such as a booklet preparedby processing the sheet bundle is improved.

1. A sheet stacking device comprising: a sheet stacking section; aholding member for holding a sheet on the sheet stacking section; adriving device for moving the holding member between a holding positionand a retreating position; and a control device for controlling thedriving device, wherein the control device sets the holding member inthe retreating position while a sheet is being conveyed to the sheetstacking section and sets the holding member in the holding positionwhen the sheet has arrived at the sheet stacking section and then setsthe holding member in the retreating position based on information ofapproaching of a subsequent sheet to the sheet stacking section.
 2. Thesheet stacking device of claim 1, wherein the information of approachingis a sheet detection signal from a first sensor equipped in an upstreamposition of the sheet stacking section.
 3. The sheet stacking device ofclaim 1, wherein the control device controls to set the holding memberin the holding position based on a sheet detection signal of a secondsensor equipped in a position which is vicinity of a receiving sectionof the sheet stacking section and is upstream of the sheet stackingsection.
 4. The sheet stacking device of claim 3, further comprising: afirst sensor equipped in an upstream position of the sheet stackingsection for transmitting a sheet detection signal which is theinformation of approaching; and wherein the first sensor detects a sheeton an upstream side of the second sensor.
 5. The sheet stacking deviceof claim 1, wherein the control device controls to set the holdingmember from the holding position to the retreating position based on astop signal for stopping the sheet stacking device and set the holdingmember in the holding position based on a stop cancelling signal.
 6. Asheet processing apparatus comprising: the sheet stacking device ofclaim 1; and a processing device for applying processing to a sheetstacked thereon.